So called scanners are used especially in the graphics industry for the pixel-by-pixel photoelectric scanning of planar measured objects. They include a measuring head which is moveable relative to the measured object in one or two dimensions, which captures the spectral remission of respectively one pixel of the measured object or object to be measured by way of a 0°/45° measurement geometry and converts it into corresponding electric signals. Scanners equipped with fiber optics are also already known, which can measure a complete image line at once. However, scanners which without relative movement between the measurement head and the measured object can measure a larger measurement surface pixel-by-pixel and with sufficient accuracy for the color measurement and under the for the color measurement generally conventional, standardized geometric conditions and are not known.
On the other hand, video cameras are used for the scanning of images or for recording purposes, which are equipped with a two-dimensional image sensor onto which the complete image to be scanned is projected by way of the camera lens so that no relative movement between the camera and the image is required. The image sensor generally consists of a two-dimensional array of light converter elements integrated into a chip, normally on CCD basis (charge coupled devices). Color enabled video cameras either have several image sensors with upstream color filters or an image converter with integrated color filters. The resolution of the scanning is fixed by the number of light converter elements available for each color channel and by the projection scale.
The geometric conditions for the color measurement are defined by international standards. For the normally used 0°/45° measurement geometry the illumination of the measurement surface is to be carried out at 45°+/−5° to the normal of the measurement surface and the remitted measuring light captured at an observation angle of 0°+/−5° to the normal of the measurement surface. The light path can also be selected to be the opposite.
It is an significant problem of the calorimetric measurement by way of a video camera of large surface measured objects that on the one hand the optical projection means cannot be made completely free of geometrical distortions at reasonable cost and produce more or less pronounced reflection images and that on the other hand scattered or adventitious light effects occur between the individual image points of the measured object or object to be measured and are measured as well because of the necessarily missing measurement shutters or other screening devices. Furthermore, especially with larger measured objects or object to be measured, the angle of incidence of the measurement light on the filters used for the spectral splitting is not the same at all image points, whereby spectral errors occur as well.